Supplementary Information Concerning P&C Insurance Operations (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Supplemental Information For Property Casualty Insurance Underwriters [Abstract]
Deferred policy acquisition costs		$ 119,660	$ 91,983	$ 79,452
Reserve for losses and LAE		2,289,727	2,202,644	2,159,634
Unearned premiums		887,344	820,676	766,167
Net earned premiums		1,100,345	984,087	935,895
Net investment income	[1]	79,413	68,571	64,092
Losses and LAE expenses incurred related to Current year		693,976	637,267	601,041
Losses and LAE expenses incurred related to Prior years		(28,528)	(64,669)	(55,812)
Amortization of deferred policy acquisition costs	[2]	165,045	129,977	127,695
Other operating expenses	[1]	230,583	220,643	196,825
Net written premiums		$ 1,186,224	$ 1,043,860	$ 1,000,138

[1] Net investment income and Other operating expenses reflect only such amounts attributable to our Company's insurance operations.

[2] Amortization of deferred policy acquisition costs reflects only such amounts attributable to our Company's insurance operations. A portion of these costs is eliminated in consolidation.